On Midsummer’s Eve, the central square in Whalton, a small village in Northern England, glows red with fire. The Baal Fire tradition—locals build a bonfire and light it up—is intended to bless the season’s crops and has continued uninterrupted for centuries. The Mari Lwyd tradition in South Wales is so old that no one knows how or when it began. In the depths of winter each year, individuals wearing sheets or sacks carry mounted, decorated horse skulls door to door, singing and hoping to be invited inside, a gesture reported…